Vacuum packaging machines are used today in a multiplicity of industrial fields. The reason is that the oxygen contained in the air has detrimental effects on the quality and preservation of products. This is therefore the reason why certain industrial processes, for example the packaging of products, are carried out in a partial or total vacuum. The packaging of products in a vacuum thus significantly reduces the possibility of their deterioration under the influence of the air.
In particular, the industries which often turn to vacuum packaging are the food industry, the cosmetic industry and the pharmaceutical industry because these industries are obliged to guarantee at all times that their products reach the consumer in a perfect state.
Consequently the vacuum packaging machines must necessarily include a vacuum source. This vacuum source (which is typically a vacuum pump) evacuates the air contained in the packaging before it is sealed. In one type of application, a modified atmosphere is injected into the packaging before it is sealed. This method is very often used in the food industry (in particular for the packaging of fresh meat) because it makes it possible to preserve the original form of the food and at the same time keep its fresh appearance, appreciated by the customers, even after a very long period of preservation.
A number of types of machines allowing vacuum packages to be produced are commonly used today. These different types of machines are distinguished in particular by the type of packaging produced, the desired structure or desired application.
One type of vacuum packaging machine which is currently widespread, in particular in the food industry, is known by the name of “tray sealer”.
A tray sealer is typically integrated in an assembly for packaging food products in trays in a plastic material or in other suitable receptacles. In such an assembly, a “train of trays” advances step by step on a belt or another similar device in a filling station in which a predetermined amount of the product is deposited in each tray. Afterwards the belt with the trays continues its path towards the tray sealer in which the trays are hermetically sealed with a protective foil before being stocked for transport and sale.
Depending upon the applications, the trays can be put under vacuum and/or filled with a gas mixture (known by the name of “modified atmosphere” or MAP) before being tray-sealed.
The “thermoformers” are another type of vacuum packaging machines. Since the thermoformers are used rather often in the packaging of medicines (tablets, pills, lozenges, etc.) in the form of blisters, they are also called “blister packaging machines.”
A thermoformer is essentially a machine which allows pieces to be made by deformation of a plastic sheet. To this end, an electrical resistance is typically foreseen to heat a plastic sheet until it becomes soft. Then a mould is used to give the desired shape to the plastic before it is cooled and extracted from the machine.
Finally, the machines called “chamber machines” work on the basis of bags of plastic material. They are very widespread in the food industry, but also find application in the packaging of other products of mass consumption, surgical instruments or similar items. In a first step, the bags are filled with the product to be packaged. Then the bags are positioned in the working chamber which is closed off by a bell before the vacuum is achieved in the bag through evacuation of the working chamber. In certain applications, a controlled atmosphere is created in the bag. Finally, each bag is sealed by thermal welding.
Of course other types of vacuum packaging machines exist which can be distinguished from these three outlined types by the type of package used.
Coming back to the different vacuum sources in these machines, central vacuum installations have been known for a long time, notably for groups of vacuum packaging machines. Such central vacuum installations necessarily make use of a network of pipes which transport the air between the packaging and the central source. Rather often these central vacuum installations comprise a multitude of vacuum chambers and reservoirs which are connected to different stages of pressure, of which each stage contains another level of pressure.
These central vacuum installations typically have large capacities, and have in particular the advantage of being able to “feed” a plurality of machines at the same time. However, their network of pipes, reservoirs and chambers is costly, very cumbersome for maintaining the desired capacity of pumping, and also very difficult to clean.
Also known is groups of pumps made up of one or more primary pumps and boosters. Typically, the primary pumps are situated outside the vacuum packaging machine, usually for reasons of congestion, in order then to be connected by a pipe to the machine. The valves of the separations and of other auxiliary elements are likewise provided in such an installation in order to enable realisation of the vacuum sought. As a general rule, the control of all the different pumps in a group of pumps of this type is achieved by means of automatic control.
The groups of pumps of this type also have the problems connected with cumbersomeness or congestion and cleaning, but it is moreover necessary to ensure the control of the different elements of the system in an optimal way, which can create problems at the level of synchronisation and/or adjustment.
Also known are the solutions in which a vacuum pump is incorporated into the housing of the vacuum packaging machine, and is directly connected to the part of the machine which must be put under vacuum. Although advantageous at the level of connection of the pump, this arrangement clearly has the disadvantage of being limited only to pumps with certain predetermined dimensions. In other words, the choice of pumps is inevitably limited, and it is thus sometimes difficult or even impossible to find a pump having the necessary features that goes well with the shape and the structure of the packaging machine.
On the other hand, the single pumps and the primary pumps in groups of pumps are in the vast majority of applications vacuum pumps of the lubricated slide vane rotary type. The operating principle of this type of pump poses the problem of drainage of fluids which is intrinsically connected to the nature of the process of pumping. This implies personnel, down times of the installations, but also the consumption of oil and its reprocessing. The operating costs are thereby directly affected.
Moreover there are great risks of contamination upstream from the products to be packaged from the oil coming from a slide vane rotary vacuum pump. This poses a problem in particular in the applications in which the items to be packaged are food or pharmaceutical products which must fulfill certain predefined hygienic standards. The damage can be sizeable considering the rate of an automated vacuum packaging machine. This necessitates a specific and fine monitoring.
Recent applications in the food industry are known where the pumps used are not lubricated slide vane rotary vacuum pumps, but are dry vacuum pumps of the screw type. These pumps originate from standard industrial pumps already proposed by the manufacturers on the market with however slight adaptations connected to the standards of the food industry.
These standards of the food industry notably call for the keeping of elevated levels of hygiene which require a regular cleaning as well as a regular disinfection of the pumps. Nevertheless access to the pump rotors of these pumps is often difficult and takes place by way of total disassembly of the pump, rendering the cleaning problematic. Likewise, the assembly of the different pieces of the pump after the cleaning also proves difficult owing to the problems of precise centring and adjustment of the rotors, which normally requires the intervention of specialized personnel.
Moreover, manufacturers continually want to reduce the cumbersomeness of the components in their manufacturing installations, and in particular in the vacuum packaging machines where the space in the plane of conveyance of the products to be packaged is restricted. At the same time they require of the pumping devices that they always perform better in terms of output and energy consumption.